CO2 equivalents

There was a minor kerfuffle in recent days over claims by Tim Flannery (author of “The Weather Makers”) that new information from the upcoming IPCC synthesis report will show that we have reached 455 ppmv CO2_equivalent 10 years ahead of schedule, with predictable implications. This is confused and incorrect, but the definitions of CO2_e, why one would use it and what the relevant level is, are all highly uncertain in many peoples’ minds. So here is a quick rundown.

Definition: The CO2_equivalent level is the amount of CO2 that would be required to give the same global mean radiative forcing as the sum of a basket of other forcings. This is a way to include the effects of CH4 and N2O etc. in a simple way, particularly for people doing future impacts or cost-benefit analysis. The equivalent amount is calculated using the IPCC formula for CO2 forcing:

Total Forcing = 5.35 log(CO2_e/CO2_orig)

where CO2_orig is the 1750 concentration (278 ppmv).

Usage: There are two main ways it is used. Firstly, it is often used to group together all the forcings from the Kyoto greenhouse gases (CO2, CH4, N2O and CFCs), and secondly to group together all forcings (including ozone, sulphate aerosols, black carbon etc.). The first is simply a convenience, but the second is what matters to the planet. Many stabilisation scenarios, such as are being discussed in UNFCCC negotiations are based on stabilising total CO2_e at 450, 550 or 750 ppmv.

Magnitude The values of CO2_e (Kyoto) and CO2_e (Total) can be calculated from Figure 2.21 and Table 2.12 in the IPCC WG1 Chapter 2. The forcing for CO2, CH4 (including indirect effects), N2O and CFCs is 1.66+0.48+0.07+0.16+0.34=2.71 W/m2 (with around 0.3 W/m2 uncertainty). Using the formula above, that gives CO2_e (Kyoto) = 460 ppmv. However, including all the forcings (some of which are negative), you get a net forcing of around 1.6 W/m2, and a CO2_e (Total) of 375 ppmv with quite a wide error bar. This is, coincidently, close to the actual CO2 level.

Implications The important number is CO2_e (Total) which is around 375 ppmv. Stabilisation scenarios of 450 ppmv or 550 ppmv are therefore still within reach. Claims that we have passed the first target are simply incorrect, however, that is not to say they are easily achievable. It is even more of a stretch to state that we have all of a sudden gone past the ‘dangerous’ level. It is still not clear what that level is, but if you take a conventional 450 ppmv CO2_e value (which will lead to a net equilibrium warming of ~ 2 deg C above pre-industrial levels), we are still a number of years from that, and we have (probably) not yet committed ourselves to reaching it.

Finally, the IPCC synthesis report is simply a concise summary of the three separate reports that have already come out. It therefore can’t be significantly different from what is already available. But this is another example where people are quoting from draft reports that they have neither properly read nor understood and for which better informed opinion is not immediately available. I wish journalists and editors would resist the temptation to jump on leaks like this (though I know it’s hard). The situation is confusing enough without adding to it unintentionally.

193 Responses to “CO2 equivalents”

Thanks for clarifying this term Gavin. Your explanation covers usage of CO2-e for atmospheric concentrations, which is what Tim Flannery was talking about, but it would probably be useful to explain its usage for emissions as well.

As I understand it, when referring to greenhouse gas emissions, “carbon dioxide equivalent” refers to the amount of carbon dioxide that would give the same warming effect as the effect of the greenhouse gas or greenhouse gases being emitted. It is normally used when attributing aggregate emissions from a particular source over a specified timeframe. It is used in this way at national and international levels to account for greenhouse emissions and reductions over time. Importantly, Article 3 of the Kyoto Protocol states targets for emissions reductions in terms of “aggregate anthropogenic carbon dioxide equivalent emissions of the greenhouse gases listed in Annex A.” [Annex A lists six gases: carbon dioxide (CO2); methane (CH4); nitrous oxide (N2O); hydrofluorocarbons (HFCs); perfluorocarbons (PFCs); and sulphur hexafluoride (SF6)].

Also, it may be a useful point of clarification to note that some authors and inventories refer to “carbon equivalents” when discussing quantities or atmospheric concentrations of greenhouse gases. Figures for “carbon equivalents” can be converted to “carbon dioxide equivalents” by multiplying by 44/12 to take account of the different molecular weights. The IPCC guidelines use “carbon dioxide equivalents” for GHG but “carbon equivalents” is more meaningful than “carbon dioxide equivalents” when discussing the amount of carbon stored in fossil fuels and sinks such as the deep ocean where the carbon is not in gaseous form.

I am not a climate scientist so could you please clarify whether my understanding is correct?

[Response: Yes, that is correct. When used for future emissions over a specific timescale – usually a century, you take the actual emission and multiply it by the Global Warming Potential (GWP) for that gas and that time period. This is good for the well mixed GHGs (CH4, N2O, CFCs) but breaks down for the short-lived species (NOx, VOCs etc.) that are ozone precursors or for aerosols. – gavin]

My reasons are solely based on the Eemian intergalcial (Termination II), about 134 kya. At that time it seems that carbon dioxide in the atmosphere peaked at about 292 ppmv (Vostok Ice Core analysis only, average of the three studies on the NOAA Paleoclimatology site). During the Eemian the sea high stand was about 4 meters higher than today’s sea stand.

I conclude that, roughly, any concentration greater than about 280 ppmv eventually leads to sea stand rise, hence we are currently in peril of eventually seeing quite a substantial sea stand rise. If so, that will be quite a calamity, even if it takes centuries to reach the highest stand.

[Response: There were other differences during the Eemian – specifically orbital configuration changes that meant that NH summers (May-Sep) were much warmer than today. Even though global temperatures were only about 1 or 2 deg warmer than now, Greenland temperatures were more liek 3 to 5 deg C warmer. So if you are looking for predictions, look for cases where Greenland is likely to be that warm (most BAU scenarios by 2100 as it happens – see Overpeck et al, 2006 Science). -gavin]

Not so sure we haven’t commited ourselves to 450 ppmv- anything lower seems entirely unreasonable from a common sense point on how things are moving along. Also would be hard to define “dangerous” levels- to some we already hit that point, but I think ~2 C warming is the beginning of where “alarming ” is. Of concern now seems to be how feedbacks will react and give us more CO2 or more warming- we’ve gotten more humid from the water vapor feedback from the latest Willett et al (Nature) paper, the decline of CO2 sinks (Le Quere et al 2007). Looks like aerosols will mitigate some warming, but I suspect that even those would decline as we get “cleaner” which ironically could give us more warming.

Sorry, I can’t follow the technical explanation too well. Are you saying that Tim Flannery has made incorrect claims that we are ahead of the predicted schedule based on his misreading of the draft report, or are you saying that the media did not accurately report what Flannery meant to say?

Thanks for giving the background to the recent statements on CO2-eq concentration, this has been raising many questions.

If I may add to your explanation though: The figure of 455 ppm CO2-eq comes from converting the value of 2.63 W/m^2 given in WG I Chapter 2, Table 2.12, for the total radiative forcing of “long lived greenhouse gases” to a CO2-eq concentration using the formula that you cite. In your calculation you added the indirect effects of CH4 on stratospheric water vapor but those were classed separately in the WG I report.

What to include, and what not, is, as you have implied, somewhat subjective, but the fact that different radiative forcing agents have very different degrees of persistence into the future, and that the shortest lived components are negative (i.e. cause cooling) is very policy relevant. If all anthropogenic emissions stopped completely tomorrow, total radiative forcing (and warming) would increase – not decrease – due to the rapid removal of aerosols from the atmosphere and the disappearance of their cooling effect. This fact underlies the difficulty that those constructing mitigation scenarios for the 21st century have in coming up with plausible ways of avoiding a warming of 2C.

Of course I agree fully with your final comments on those who leak material from draft IPCC reports. This is usually done inaccurately and out of context. In this case reference to the radiative forcing projections given in the Third Assessment Report shows that there is no basis for saying that long lived greenhouse gases are now 10 years ahead of the projections of a few years ago.

“The risks of the worst impacts of climate change can be substantially reduced if greenhouse gas levels in the atmosphere can be stabilised between 450 and 550ppm CO2 equivalent (CO2e). The current level is 430ppm CO2e today, and it is rising at more than 2ppm each year.”

The same report shows a 50% chance of a 2 C increase if with a 450 ppm stabilization.

If you’re referring to total forcings, then what is the 50% chance of a 2 C atmospheric level?

[Response: Stern used CO2_e (Kyoto) for today’s level, but CO2_e (Total) when discussing stabilisation scenarios. They shouldn’t have been compared like that. Using a standard sensitivity, 450 ppm gives about 2 deg C – so if you think that we are as likely to be greater than that as less than that (reasonable guess), then 450 ppmv is indeed the level that gives us a 50% chance of avoiding > 2 deg C. – gavin]

In particular, as I understand it a reduction in fossil fuel use will lead to a reduction in emissions of aerosols (the majority of which have a cooling affect). Aren’t the atmospheric lifetimes of these aerosols far shorter than that of the warming gases. Won’t this result in a situation where as we reduce CO2 emissions, some of the current cooling effect will be reduced, while most of the current warming effect remains?

Does your analysis above assume that the total cooling effects of aerosols do not decline?

The low value of CO2eTotal is less comforting if the negative forcings arise from the same activities as the positive forcings (e.g. dirty coal combustion). Then measures that reduce CO2 emissions or clean up local air pollution reduce the masking effects on a short time scale, while long-lived gases remain in the atmosphere, so that CO2e would rise rapidly. This effect would seem to make the headroom between 375 and 450 somewhat illusory.

[Response: You are absolutely correct. I was just about to enter my own comment to this effect, but you have done it for me. David]

Data quality analysis as reported in IPCC WG1 Chapter 2 is not adequate for risk assement data used for decisions affecting large populations. In risk analysis, we are not talking about the fate of clouds, we are talking about the fate of people. We need data of known quality! Data with “wide error bars” does not qualify. At the very least, we need a numerical estimate of how wide those error bars are. That number is not in the text, I do not see a protocol for calculating such a number, or the raw data that could be used in such a calculation. I was on the ASTM Technical Committee for Data Quality for Human Health Risk Assessment. I know that numerical estimates of data quality are not easy. Worse, I know what a blow to the ego such an analysis can be, But, this site is not about “easy”. This site is about honest and correct.

If we do not have good estimates of the error bars, then we need to apply safety factors; as we did when we started doing human health risk assessments of National Priority List hazardous waste sites. Put in a safety factor, and 375 might well become the new 450. Certainly, Gavin might not like that when it is first presented to him. But, if we are considering something that affects 6 billion people, then being only 99.9999% certain says that we do not care about an event that kills three times more people than 911. If we are only 99% certain then, we can expect 70,000,000 to die as a result of our ignorance. How many people’s lives are we willing to lose because we did not do our homework on data quality?

I am not advocating zero risk. I am saying, “Let’s make decisions based on knowledge.”

I guess this has to be clarified. Was Flannery talking about forcing or greenhouse gas concentration? I think it was the latter. If that’s the case, as people at the Hadley Center have shown, we are already at a concentration of over 450ppm of carbon dioxide equivalents, which is dangerous. Yes, you have aerosols and other factors, but we have no clue how much of a cooling effect they’re actually having. We also know that they will probably be gone in the next 10-20 years. After that happens, the full forcing of greenhouse gases currently in the atmosphere will show, pushing us beyond 2C. It’s also important to mention that we have a 50% chance of avoiding 2C if we keep concentrations (of greenhouse gases minus the cooling) at current levels. Because of keeping these things out of discussion, people are setting absolutely wrong targets (i.e. halving world emissions by 2050).

Gold standard work as ever Gavin. I think the fact that this level is within reach is disturbing enough under any scenario, but the damage occurs when AGW realists like Flannery who is already pilloried by the usual suspects, reach too far beyond the data.

I think the IPCC estimates are biased conservatively, as usually is the case in science, but journalistic hyperbole does the issue a great disservice and makes weakens the effort to turn this thing around. We don’t need that.

Holly, I think the problem is the journalists have no one to verify any claims that their source is quoting from a discussion draft. The people who do know what’s in the drafts and comments have promised not to leak them.

The last round there was a lot of stuff in the press that didn’t turn out to be right.

[Response: Michaels doesn’t bother to notice that RC actually doesn’t have anything to do with Hansen (whose personal thoughts on climate are available here). Hansen’s (and my) peer reviewed output is available at http://pubs.giss.nasa.gov , and I don’t think that Jim is a slouch in that department. – gavin]

I’d really appreciate a comment of Gavin in the light of contributions #9, 10, 11 and 12. As Gavin himself stated in his response to contribution #1: GWP calculation for specific time horizonts is good for long lived GHGs but breaks down for short-lived species (e.g. aerosols).

1.) Thanks for this post, as it (once again) makes clear for those laymen like me,

– how difficult it is to put emerging chunks of research information into its place even for scientists who are not immediately involved

– how easily you can achieve a (not even intentional) distortion of research results into facts without proper context, with all the possibly disastrous impact on the broader public.

2.) I’d really appreciate a similar assessment of ‘thawing permafrost’ or ‘melting’ in general.

Several times I stumbled over the assertion, that there are no surprises to expect from thawing permafrost or, recently, accelerated melting in Greenland as well as in Antartica.

At least, those Dansgaard-Oeschger events did happen. And the record minimum arctic sea ice this year definitely shows what is meant by ‘highly nonlinear behaviour’. So I am curious why permafrost thawing should not involve some nasty surprises.

Good article, but one fact that I think is missing is the choice of time horizon for the Global Warming Potentials (GWP) and the consequences for the calculation of CO2 equivalent emissions.

IPCC reporting obligations still require the use of the older IPCC Second Assessment Report (SAR) 100-year horizon GWP for national inventories, defining a quasi “standard” for comparable CO2 equivalent emissions / total greenhouse gas emissions.

But IPCC papers such as WG1 Chapter 2 (link in the original article, table 2.14, page 212) give different GWP for 20, 100(!) and 500 year horizons alongside the 100 year SAR values, making it hard for laymen (and even experts, sometimes) to find out which GWP to use for calculations.

The Norwegian Nobel Committee has decided that the Nobel Peace Prize for 2007 is to be shared, in two equal parts, between the Intergovernmental Panel on Climate Change (IPCC) and Albert Arnold (Al) Gore Jr. for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change.

But a lot of the “negative” radiative forcing components have atmospheric residence lifetimes of ~week, so are irrelevant to a discussion of CO2_e levels in terms of reaching a stabilisation target.

Isn’t that obvious?

[Response: No. The reason why is that even with that short residence time, continual emissions mean that atmospheric levels stay elevated – contributing to long term changes. It is true that efforts to reduce aerosols (including black carbon) have immediate effects as opposed to CO2 emission cuts which take a while to make a difference to concentrations. – gavin]

Congrats on winning the Nobel peace prize to Al Gore, the IPCC, and all of you folks that have contributed towards the research and the reports. AGW-naysayers will sooner or later run out of their excuses.

Response to #24 – I accept that. On a narrow point of what the instantaneous forcing is equivalent to, then, yes, you obviously have to include the short-lived aerosols.

However, if we ever get to a stable level of CO2, we won’t be emitting sulphate aerosols any longer, or burning vast areas of rainforest (emitting black carbon). In the context of how close we are to various stabilisation targets, then, I think it makes sense to discount short-lived agents whose release is associated with anthropogenic sources of GHGs.

Of course, this also means that you can have an overshoot scenario. In CO2_e terms you could go over the stabilisation target, but move back down to it by reducing levels of the shorter-lived GHGs such as CH4 and NOx. In that sense the non-CO2/CFC part of the CO2_e is not committed to the same extent. (And the fact that CO2_e(Kyoto) ~455ppmv is not quite as alarming).

If it helps, I’m thinking of a timescale for stabilising GHG levels by 2050.

Please address these simple questions for me, as an intelligent layman concerned about the future of our planet and our children:

1. Even the food we produce and eat is not carbon-neutral, considering the huge amounts of fossil fuel used for producing fertilizers,irrigation,transportation,refrigeration,cooking, etc that go into the food production-consumption chain.

2. Where is the carbon sink that can absorb the CO2 of other man-made consumption processes like automobiles, electricity, aeroplanes,trains, airconditioning, heating,manufacturing, mining etc. which are colossal and their effects cumulative?

3. It appears to me that we are doomed like the mythical ICARUS whose wax-fixed wings melted as he showed off his flying before the sun. In short, no amount of fossil-fuel burning – no matter how less – is ultimately sustainable from the point of view of preventing accumulation of CO2 and waste-heat in the environment, and an eventual over-heating and melt down of the planet.

4. Possibly, human knowledge, wisdom, compassion etc. – and a big dose of humility – may show us the path for a sustainable future, based on essential human needs and not human greeds, as Gandhi pointed out long time ago. Has anyone modelled such a future for some 10 billion humans/animals living on this earth – the life-style they can live without destroying the planet ?

Fair is fair. Shouldn’t Al Gore send a thank you note to all the right-wing nutjobs who have abandoned the scientific high ground and left him standing there alone. I mean after all, without climate change (which to be fair, he was among the first to embrace), he would just be another washed up politician. Now he has an Academy Award, a Nobel Peace Prize and bookies have cut the odds on his becoming President from 10:1 to 8:1. He couldn’t have done it without the editorial board of the Wall Street Journal, Senator James Inhoff, Rush Limbaugh, The Cato Institute, Exx-Mob etc. Come on guys step up and take a bow!

Re different time constants, I believe that is considered when calculating CO2_e.

Thanks, Gavin, for this clarification — I hadn’t checked the numbers for the Stern Review to see if they were internally consistent. Much steeper reductions would be needed to stabilize at 450 ppm if we’re already at 430 ppm, except that we’re already at 460 ppm.

RE: 12 Aerosols from combustion sources will probably not be reduced to climatologically insignificant levels before 2050. That said, any forecasts need to take into account that their influence will be reduced a few percent every year. Thus, we will get to the 450ppm threshold sooner (say 2030 and not 2050) rather than later as the well mixed GHGs continue to increase in concentration. Tropospheric ozone will also decrease, helping a little bit. Due to the long lead times in developing and installing new energy sources, it is doubtful in my mind that we still have time to avoid the 450ppm level. Taking that into consideration, a prediction today that we are committed to passing a dangerous threshhold is not unreasonable.

I pointed out the error concerning RC in Pat Michaels’ American Spectator article to him and he told me that he contacted the Spectator about it to have it corrected. So, presumably (hopefully) that will happen.

How good are the negative and positive forcing predictions in the emission scenarios climate modelors use? Hansen’s paper on where we are is good, but how predictable is the future? Specifically, how good are predictions about the timing of the clean up and then phase out (or beginning of CO2 sequestration) of coal fired power plants? Do the scientists involved think they have a good handle on how this will play out or is it a huge source of unpredictability in terms of future temperatures? What if this story’s actions play out in China and Russia? Do these governments have a plan they haven’t shared? Do the industries that seem to run (at times) our governments have a plan they haven’t shared? Should climate modelers be pouring over the minutes of board meetings?http://www.msnbc.msn.com/id/21198255/
810,000 tons of pollutant reductions, 79% reduction in sulfur emissions, 69% reduction in nitrous oxides. Two opposing forcings being reduced simultaneously. Sorry, shouldn’t have had that extra cup.

Now the mean radiative forcing since 1850 is 1.6W/m2.
We can say that the correspondant temp increasing is 0.8°C.
We can say also that there is some 0.4-05°C “in the pipe”.
Thus about 1.25°C in some decades.
The consecutive sensitivity is something as 0.78°C.m2/W.
With this sensitivity, for 450 ppm of CO2, we get a temperature increase of 2.63W/m2 * 0.78°C.m2/W = 2.06°C.
OK?
My problem is the “0.4-0.5°C in the pipe” which depends on oceanic thermal inertia.
If this inertia becomes very very great, the ocean keeps the heat and the temperature increase no more.(at least as far as complete absorption of CO2)
In this perspective what do you think about the SH ocean cooling since 2003?

“Holly, I think the problem is the journalists have no one to verify any claims that their source is quoting from a discussion draft.”

IMHO, another ongoing problem with the media is the lack of verification due to budget cut-backs. No more double and triple checking. Worse, in a very competitive “what have you got now?” market designed around sound bites and 30-second info-clips, the need to be the first to run with a story is subsuming accuracy in favor of profit.

This is one of the reasons the climate “skeptics” are able to keep their game running.

Ahhh, so what is being said here is that all things considered via +ve and -ve forcings currently add up to Co2_e of 375 ppmv of net forcing. Does this mean that we need to continue polluting to soem degree or does coal do both for us anyway regardless?

“….the mechanism triggering cooling over the region north of the Ross Sea is changes in the ocean circulation over the subdued warming region. Because the cooling in a warming climate is highly localized, it is important to analyze the oceanic processes on regional scales. Here we examine oceanic changes, focusing on the regional processes underlying the regional coolings in response to increased atmospheric GHGs forcing in the CCSM3…. ”

American right wing talk radio is spinning up the lies and usual misinformation about Global Warming and Climate Change. Neil Boortz carried on for an hour this morning about how it’s all a lie forged by the anti-Corporatists. Meanwhile, in North Georgia there only remains about 3 months of water in most of the reservoirs. These people can’t believe their own eyes, much less scientists.

Question: I have heard skeptics make the claim that many models use a future co2 rise of 1% increase per year, which is higher than co2 is actually rising. I assume they are confusing co2 increase with co2_e increase when they make this claim (?)

[Response: 1% CO2 growth is just a standardised scenario that modellers use so that everyone does the same run, like 2xCO2 – it’s not a prediction. There are lots of more ‘realisitic’ scenarios that are done that have growth rates closer to observed and include all the other factors (like methane, aerosols etc.). – gavin]

re 14
“Holly, I think the problem is the journalists have no one to verify any claims that their source is quoting from a discussion draft.”
re 35
“IMHO, another ongoing problem with the media is the lack of verification due to budget cut-backs. No more double and triple checking. Worse, in a very competitive “what have you got now?” market designed around sound bites and 30-second info-clips, the need to be the first to run with a story is subsuming accuracy in favor of profit.”

I doubt it is entirely that innocent. If you know any journalists at all, then you are fully aware that advocacy reporting is the purposeful objective of many.

[Response: I know many journalists and that is as far from the truth as it is possible to be – especially when it comes to science issues. – gavin]

Catman306,
Capitalists tend to be rational creatures. They will continue to ignore reality as long as it is profitable. As long as those royalty checks from Exx-Mob. keep roling in, they can save up to buy the house on the hill and they don’t need to worry if the rest of the town floods. I think it is important for them to realize that they have handed a very powerful issue to their political enemies. It’s gotten their nemesis Al Gore an Oscar and now a Nobel Prize. Bookies have reduced his odds of becoming president from 10:1 to 8:1. The Truth is a powerful weapon even when it is inconvenient.

re 29
“…Shouldn’t Al Gore send a thank you note to all the right-wing nutjobs who have abandoned the scientific high ground…”
re 40
“…right wing talk radio is spinning up the lies…”

I am not scientific and I am one of those you are trying to convince. But when you (and others) use language like that (or find it necessary to whitewash or deny tenure to disagreeing colleagues) I tend to wonder whether you fear your view is indefensible.

The anti’s include reports from the many scientists, including from Canada and Europe, (your colleagues) that point out logical discrepancies that the “for’s” never seem to address other than by denigrating name calling. So who am I supposed to believe, the anti’s, or the name-callers?

The “other” viewpoint should have equal prominence in the news, and I mean equal. But it doesn’t. That fact alone raises red flags.

The “we must prevent the earth from warming” viewpoint predominates in the news, yet no one has ever explained to me why. I remember from elementary school how the earth once had no ice at the poles and the fossil record in northernmost land shows it was tropical, yet the earth wasn’t flooded. Why?

No one has explained why the current warming trend isn’t just another harmless 200-yr cycle. Do we deny cyclical warming and cooling trends?

No one has explained to me why the news a generation ago was constantly lamenting a cooling earth with the same fervency they now lament its warming. Were they wrong then and right now? Or wrong now and right then? Or neither?

On the other hand, that some slight warming has been detected I can accept, but given that, why does it follow that “man” has to do something about it? Why can’t we just live with it?

That is why the subject is debatable, it has nothing to do with “right-wing” which I thought was a political term (and I don’t like politics).

[Response: None of your objections have any validity, I’m afraid – that’s why when they get brought up over and over again, even though they have been debunked dozens of time, people get frustrated. I suggest that you look each of these points up over at Coby Becks guide, or the New Scientist Climate Change Myths page (linked from the ‘Start Here’ page). If you still think these are truly debatable issues, come back and we can discuss. – gavin]

Vinod Gupta (28) — These topics, while interesting, are rather off-topic for Real Climate. There are many alternative sites listed in the sidebar under the heading Other Opinions. Some of those may be of more assistance to you.

Speaking of Hansen, he’s been pilloried in certain quarters for over-predicting sea-level rise for this century. But see this article and this release regarding a new paper (not actually published yet AFAICT, but the GRL draft is available for those who have that subscription):

“Greenland is melting at record speed

“The inland ice on Greenland is vanishing much faster than scientists previously believed. This can be seen from new research results from the Danish National Space Center.

“Each year, in the south eastern part of Greenland alone, the glaciers produce a mass of icebergs which is equivalent to a gigantic ice cube measuring 6-1/2 km on all sides. And the reduction of the inland ice is accelerating. At the moment, four times as much inland ice is disappearing compared to the beginning of the decade.

“‘If this development continues, the melt water from the inland ice will make the world’s seas rise by more than 60 cm this century’, says senior researcher Abbas Khan of the Danish National Research Center, who was responsible for the research project. The results were obtained in co-operation with the University of Colorado and have just been published in the international research magazine Geophysical Research Letters.

“The researchers have measured the rate of melting with special, highly sensitive GPS stations placed on the mountains along the inland ice. When a quantity of inland ice disappears, the pressure on the surrounding mountains eases and they therefore rise slightly. This can be measured by the GPS stations. The measurements show that the mountains along the fast glaciers in south east Greenland are rising by 4-5 cm a year. Meanwhile, the rim of this inland ice will be 100 m thinner a year.”

A question – Why do GWPs vary with the time scale used time constant used? Wouldn’t the radiative forcing of the molecule, multiplied by it’s average lifetime in the atmosphere, give a GWP that is independent of time (as long as the time scale is long enough)? Or is it that we’re only looking at a time frame that is much longer than average lifetime of the gases?

Vinod Gupta: #28 There are answers. 1. We all eat vegan diets, with the plant foods grown organically. 2. We get all our power from solar, wind, geothermal, waves, etc. No fossil fuels at all. This can be done. All we need to do is do it.